Effect Of The Different Nitrogen Content In Welding Wire On Microstructure And Mechanism For Hybrid Welding

Appropriate solid-solution nitrogen content is the prerequisite for good performance of high-nitrogen steels.But during the welding process of high-nitrogen steels,the phenomenon of nitrogen loss of austenite solid-solution nitrogen often occurs.Therefore,the research and development of a new type of high nitrogen austenitic stainless steel welding wire and its application in the welding of high nitrogen steel can ensure that the solid solution nitrogen content of the weld is the same as or similar to that of the base metal,which is the precondition for ensuring the performance of the welded joint.In this paper,8mm thick high-nitrogen steel plate was used as a test material,and a rated power of 4kW of Nd: YAG solid laser was used to carry out the laser-arc hybrid welding.Firstly,the microstructure and microstructure evolution of joints after welding with nitrogen-free welding wire were studied.Based on this,the effect of the nitrogen content of the welding wire on the microstructure of the joint after welding and the mechanical properties was studied by changing the nitrogen content of welding wire,thus preliminarily revealing the transition mechanism of molten pool of the nitrogen element.The results of the study showed that when nitrogen-free welding wire was welded,the transition form of the droplet is almost a continuous jet transition,and there was basically no“burst” phenomenon of the droplet,but as the nitrogen content of the wire increased,the welding arc gradually increased,and the "burst" phenomenon of the droplets in the transition process became more and more obvious.With the increase of the nitrogen content of the welding wire,the formation of the weld surface was improved,but the excessively high nitrogen content of the welding wire would cause a certain welding spatter.The joint cross section of the welding wire with different nitrogen content after welding was a "high foot cup" shape with the upper wider and the lower narrower.The solidification patterns of the welds with different nitrogen content are all in AF mode and the microstructure of the weld is austenite and a small amount of ferrite.The nitrogen content of the weld increased with the increase of the nitrogen content of the welding wire.The content of ferrite in the weld decreased with the increase of the nitrogen content of the welding wire.A black “etch pit” occurs in all welds due to corrosion,and the number of pits increased with the increase of nitrogen content of the weld wire.The hardness of the weld zone is the lowest,the hardness of the base metal zone is the highest,and the hardness of the heat affected zone is between the two poles.With the increase of the nitrogen content of the welding wire,the hardness of the weld zone decreased.After the welding without adding nitrogen(0.0N)and with 0.4N welding wire,the pores are large and concentrated,and after adding 0.2N and adding 0.6N welding wire,the internal pores are relatively small,with the pores are all distributed in the vicinity of the fusion area.In the welding process,the nitrogen element in the welding wire was dissolved in the weld seam in the form of nitrogen atoms,some of which remained in the weld seam in the form of nitrogen pores,and some of them escaped as nitrogen.